280 CHAPTER 10 The Immune System Lymphoma involves a class of cells called lymphocytes. If you have lymphoma , it means that, at some point, somewhere in your body, a lymphocyte made an error in copying the genetic information that directs how that cell was supposed to look and behave. When the cell reproduced itself, it passed this error on to its daughter cells. After several such genetic errors accumulated, the cell’s descendants became malignant, or cancerous, cells. They no longer played by the rules that allow all the cells of the body to work together in harmony. Instead they became dangerous and destructive. As with many forms of cancer, the behavior of malignant lymphocytes echoes the behavior of the normal cells from which they arose. Malignant cells in the different kinds of lymphoma can resemble normal lymphocytes at different stages of development. Therefore, understanding how lymphocytes normally develop and function helps us understand the behavior of the abnormal lymphocytes found in lymphoma. This understanding has also helped researchers design therapies that target lymphoma cells. Lymphocytes are an integral part of the immune system, which consists of various different cell types and tissues that work in concert to defend us from disease. While understanding how normal lymphocytes behave helps us understand lymphoma, understanding the function of the other cells that make up the immune system is less directly relevant. However, a basic understanding of immune system function is useful to people with lymphoma for several other reasons. First, many of the therapies used to treat lymphoma affect other cells in the immune system. Understanding the basics of immune system function will help you understand the potential side effects of these treatments. Sec- The Immune System 281 V ond, some of the exciting new approaches to treating lymphoma, such as those using monoclonal antibodies or cancer-specific vaccines, depend on recruiting your own immune system into the fight. Basic immunology will help you understand how these therapies work and why they are more specific than older approaches to therapy. Finally, understanding the immune system is key to understanding the immune surveillance hypothesis of cancer. This hypothesis, which has received a lot of publicity in alternative health circles, suggests that malignant cells continually arise in our bodies but are kept in check by our immune systems. Many people believe that stimulating the immune system should be beneficial if you have cancer, and these people may be interested in taking herbs and supplements that they hope will do this. Once you start thinking of the immune system as consisting of a group of different types of cells rather than as an abstract notion, however, you might question whether taking such substances, without understanding exactly what they’re doing and where they’re acting, is a good idea for someone with a cancer of the immune system itself, such as lymphoma. This chapter focuses on understanding the immune system and how it works, paying particular attention to lymphocytes and those aspects of immune system development and function that are relevant to lymphoma and its treatment. Chapter 9 provides an introduction to cell biology and current ideas about cancer; the concepts introduced in that chapter may be helpful in understanding this chapter. General Overview of the Immune System Our immune systems allow us to remain healthy in what might otherwise be considered a hostile, germ-ridden world. Without an immune system, our bodies would be easy prey for the multitudes of pathogenic (disease-causing) organisms that surround us. Our cuts would routinely become infected, and we’d have no better defense against mold spores than does the half-eaten peanut butter and jelly sandwich your four-year-old slipped behind the radiator a week ago. With an immune system, though, we do a remarkably good job of coexisting with most of the microorganisms we encounter. In the broadest sense, the immune system includes such organs as the skin and the mucous membranes that line the airways and the gastrointestinal tract (stomach, intestines, and associated structures). These are the first lines of defense against potentially harmful invaders. However, the immune system is usually considered to consist of the cells involved in an active response U 282 Understanding Lymphoma to potentially harmful microorganisms rather than those that simply form a barrier to invasion. These actively responding cells include different types of white blood cells that circulate in the body’s two interconnected vascular systems (the circulatory system, which carries blood, and the lymphatic system , which carries a...

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